Just read that an outgoing Director of the giant Calpers pension plan (state of California) went on the record to say that the plan is on the verge of insolvency. That is obviously a huge deal given the number of people this plan represents (~ 1.6 million). His comments are backed up by the fact that fund administrators have recently outlined a number of changes in an effort to improve the numbers. One of those changes requires the groups that Calpers represents (the state, municipalities, agencies, etc) to commit significantly more funds annually in helping shore up the plan's underfunded status. The problem, however, is that many of these groups cannot afford that greater commitment. A number of California cities are on the edge of bankruptcy themselves. This mandate could create a tipping point for some. 4 Cali cities have already declared since 2008, and with 6 more rumoured to currently be at significant risk.
This is a problem that will not likely be confined to California-based pension plans. Many public and private (corporate) plans are similarly under water. Particularly true if interest rates continue to be kept artificially low going forward.